1. Field of the Invention
The invention pertains generally to direct current (DC) electric motors.
2. Description of Related Art
As is known, a DC electric motor is a machine which converts DC electrical energy into mechanical energy. Typically, such a motor includes a rotor and a stator, with the rotor rotating relative to the stator during the operation of the motor. The desired mechanical energy is typically delivered via a shaft connected to the rotor.
The rotation of the rotor relative to the stator is achieved by interacting one or more DC current-carrying coils with one or more magnetic fields. By way of example, in one configuration of a conventional DC motor, the stator is provided with, for example, two magnetic pole pieces (i.e., permanent magnet pole pieces or electromagnet pole pieces), used to produce a stationary magnetic field within the stator. The rotor, which is rotatably mounted within the stator between the pole pieces, is provided with two or more electrical windings which are connected via a commutator (a mechanical rectifier) and brushes to a source of DC power. In operation, the commutator serves to periodically reverse the flow of DC current supplied to the windings, resulting in a unidirectional torque on the windings, and thus on the rotor.
In an alternative configuration, it is the rotor which is provided with the pole pieces and the stator which is provided with the windings. As depicted in FIG. 1, such a stator 10 typically includes a central yoke 20, to which is connected two or more angularly spaced tynes 30, each of which includes a lower leg 35 and a transverse upper leg 40 connected to the lower leg. As is conventional, the upper legs 40 are discontinuous, i.e., physically separated, to permit electrical windings 45 (only one of which is depicted in FIG. 1) to be readily wound about the lower legs. These windings are, in turn, connected to a source of DC power via, for example, a commutator and brushes.
DC motors are currently used in a variety of applications, typically where AC power is unavailable. One such use is, for example, in powering the fans employed in automobiles.
Significantly, DC motors are typically much noisier than, for example, AC motors. Until recently, the noise produced by DC motors was not considered significant. However, noise reduction has now become an important factor in a variety of applications. For example, the manufacturers of luxury automobiles are now demanding DC motors which are much quieter than conventional DC motors. As a consequence, relatively quiet DC motors are now being sought.